Stainless steel weld finishing by the numbers

Abrasive disc selection, use, and safety

As the demand for stainless steel increases, welders and metal fabricators need to understand how to obtain the proper finish.

When aesthetics count, achieving the
right fi nish on stainless steel is
important. (Photo courtesy of
Norton/Saint-Gobain, Watervliet, NY.)

The use of stainless steel in North America continues to grow in popularity for industries such as appliance, food processing equipment, aerospace, and medical. In some stainless steel applications, weld grinding is required as one of the last steps for finishing. As the demand for stainless steel increases, welders and metal fabricators need to understand how to obtain the proper finish.

Standard mill finishes usually are applied to flat-rolled stainless steel directly by the manufacturer. The fabricator then applies a final finish to the welded surface to achieve the desired aesthetic appearance.

Some of the most commonly used final finishes are:

#3 — Coarse abrasive finish applied mechanically.

#4 — Brushed finish.

#5 — Satin finish.

#6 — Matte finish (brushed but smoother than #4).

#7 — Reflective finish.

#8 — Mirror finish.

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Here are some tips and guidelines for selecting and using the best abrasives product to create the desired finish.

#3 Finish

This coarse abrasive finish, #3 typically is used for stock removal. It usually requires a coated abrasive fiber disc or flap disc. Both types of discs have a ceramic grain and are most effective when applied by an angle grinder with power of more than 1,200 W.

Fiber Discs. Fiber discs remove excess material from flat and contoured surfaces with a fast initial rate of cut. A 50-grit ceramic fiber disc applied at a 10- to 15-degree angle can remove the weld quickly and produce a workable surface finish.

A hard backup pad can be used to help increase disc life and to achieve aggressive stock removal when coarser grits such as #24 or #36 are used. The hard ceramic grain helps increase cut rate and disc life. The backup pad also helps reduce heat at the point of contact, which is important for grinding stainless steel.

Flap Discs. Flap discs remove heavy weld seams and excess materials while providing long abrasive life. A 40-grit ceramic flap disc is recommended for general use. For speed and aggressive stock removal, a T29 conical disc is a suitable choice, while for blending and smooth cuts, a T27 flap disc is preferred.

FIGURE 1
Changes in any product specification can affect the surface finish on the
workpiece and thus the choice of disc. The arrows signify trend direction;
arrow length does not indicate that the effect of each factor is equal.

Flap discs provide a consistent finish with no need for a backup pad. They store without curling, offer reduced loading, and have a long disc life to reduce the number of required disc changes.

#4 Through #8 Finishes

Finishes #4 through #8 typically are used for blending and refining. Nonwoven abrasives usually are recommended, depending on the application.

Nonwoven discs can perform deburring, blending, and finishing to reduce the number of steps required. They provide a controlled, sustained finish and prevent undercutting and gouging. Their cool grinding action helps minimize the chance of warping or discoloration. They also offer low vibration and low noise.

Proper selection and usage of coated abrasive and nonwoven products help optimize the required finish on stainless steel surfaces. Changes in any product specification can affect the surface finish on the workpiece and thus the choice of disc (see Figure 1). The effect that different abrasive characteristics have on a material also factors into disc selection.

Unified Wheels. Nonwoven unified wheels remove the grind lines left on the surface by a fiber disc. Unified wheels designed for light stock removal are suitable for blending applications and can leave a bright finish.

A coarse-grade blending disc can be used in preparation for coatings, such as paint, or polishing. However, it is recommended to use the finest grade of abrasive that gets the job done, as finer grind lines are easier to remove than deep ones.

Tips for Safe Use of Coated Abrasives

When using coated abrasive discs for weld finishing, be sure to follow all the safety rules set by your employer and governmental agencies. Following are additional tips to help ensure safety and long abrasive life:

Start the tool just off the workpiece and bring it up to full operating speed before grinding or sanding.

Always ease the disc into the workpiece at a 5- to 10-degree angle to the surface.

Look for and avoid any areas on the work piece where the disc may become caught or jammed.

When grinding depressions, moldings, lips, and heavy welds, move the grinder away from the work area and not into it.

Don’t allow a disc used for heavy stock removal to rest flat on the workpiece; if you do, the whole tool assembly could be thrown into a rough, jumpy mode.

Work the disc gradually into a jagged surface before allowing the edge of the disc to bite into it. This will prevent breakage of the disc edge.

Secure small, movable workpieces before grinding or sanding to prevent them from moving when the abrasive makes contact.

Grind or sand in well-ventilated areas.

Direct sparks away from your body and away from bystanders.

Do not grind near flammable materials.

Do not wear loose-fitting clothing.

Do not store or rest the grinder/sander on the disc and pad.

Do not place the grinder/sander down un-til the disc has stopped rotating.

If you drop the grinder/sander, replace the backup pad and disc before using it again.

Avoid physical contact with the rotating disc or backup pad.

If chatter or vibration occurs during use, stop the tool at once. Determine the cause of the problem and correct it before continuing.

When using a nonround disc and backup pad, avoid tight corners and other areas where the disc can catch.

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